Conventionally, as a structure for opening and closing a fuel filler opening of a filler pipe which communicates with a fuel tank of a vehicle or the like, for example, the invention disclosed in Patent Document 1 has been known. As shown in FIG. 6A, a structure for opening and closing a fuel filler opening 1 includes a cylindrical portion 3 having both ends opened, a main flap 4 and a dust flap 5 (a first valve device and a second valve device in Patent Document 1) arranged in the cylindrical portion 3. The main flap 4 and dust flap 5 are made as a single valve in a circular plate shape, respectively. The main flap 4 and dust flap 5 have a hinge 4a and a hinge 5a with springs, respectively, about which the flaps 4, 5 can be opened and closed.
The inner end of the cylindrical portion 3 is connected to a filler pipe 2, and a fuel filler opening 6 in an annular shape is connected to the outer end of the cylindrical portion 3. As shown in FIG. 6B, when a fuel gun 7 is inserted into the filler pipe 2, the fuel gun 7 pushes the main flap 4 and dust flap 5 open. On the other hand, as shown in FIG. 6A, when the fuel gun 7 is removed from the fuel filler opening 6, the flaps 4, 5 are closed respectively by the springs of the hinges 4a, 5a under the restoring force.